1. Field of the Invention
The present invention relates to a rotor for a motor and, more particularly, to a rotor for a motor of an inner rotor type.
2. Description of the Related Art
Motors generally include an outer rotor type and an inner rotor type that is superior to the outer rotor type in rotational stability. Thus, inner rotor type motors are superior to outer rotor type motors in fulfilling the needs of heat dissipation in the design trends of high speed, integration of functions, and miniaturization.
There is a plurality of conventional inner rotor type motors. FIG. 1 shows a conventional rotor 5 for an inner rotor type motor. The rotor 5 includes a shaft 51 and a magnet 52. The magnet 52 includes a central axial hole 521 through which the shaft 51 extends. The shaft 51 can be in tight coupling with the central axial hole 521 of the magnet 52. However, the magnet 52 is liable to break. In another approach, the shaft 51 is bonded by adhesive to the central axial hole 521 of the magnet 52. However, the adhesive is liable to lose its adhesiveness due to deterioration, resulting in disengagement or undesired rotation of the magnet 52 from or relative to the shaft 51.
FIG. 2 shows a conventional rotor 6 for an inner rotor type motor disclosed in Taiwan Patent Application No. 97104952. The rotor 6 includes a shaft 61, a plurality of magnet retaining plates 62, at least two magnets 63, and two washers 64. The magnet retaining plates 62 are stacked around the outer periphery of the shaft 61 and each have at least two retaining grooves 621 for securely receiving the magnets 63. The washers 64 sandwich the magnet retaining plates 62 and the magnets 63. Due to the arrangement of the magnet retaining plates 62 and the washers 64, the magnets 63 will not disengage from the shaft 61. However, the rotor 6 solves the disadvantages of the rotor 5 at the cost of a complicated structure, resulting in inconvenience in assembly.
FIG. 3 shows a conventional rotor 7 for an inner rotor type motor disclosed in Taiwan Patent Application No. 971178192. The rotor 7 includes a shaft 71, a magnet 72, and two fixing seats 73. The magnet 72 includes a central axial hole 721 through which the shaft 71 extends. The fixing seats 73 are in tight coupling with the shaft 71 and sandwich the magnet 72, fixing the magnet 72 in a predetermined location. By the arrangement of the fixing seats 73, the magnet 72 is prevented from disengaging from the shaft 71. However, the fixing seats 73 for sandwiching and fixing the magnet 72 cause limitation in the compact design of the rotor. Namely, the rotor 7 is still complicated and inconvenient to assemble.
FIG. 4 shows a conventional rotor 8 for an inner rotor type motor disclosed in Taiwan Patent Application No. 97135497. The rotor 8 includes a shaft 81 and a plastic magnet 82. The shaft 81 includes an outer periphery having a positioning portion 811. The plastic magnet 82 is formed by injection molding to envelop the outer periphery of the shaft 81 with an inner periphery of the plastic magnet 82 engaged with the positioning portion 811. Although enhanced engaging stability is provided between the shaft 81 and the plastic magnet 82, the outer periphery of the rotor 8 must be processed to form the positioning portion 811, leading to inconvenience in manufacturing of the rotor 8. Furthermore, the engaging area provided by the positioning portion 811 is limited. Namely, the resultant engaging stability between the plastic magnet 82 and the shaft 81 is still insufficient.
FIG. 5 shows a conventional rotor 9 for an inner rotor type motor disclosed in Chinese Patent Publication Application No. CN201118294. The rotor 9 includes a magnetic hub 91, an engaging member 92, and a shaft 93. The magnetic hub 91 and the shaft 93 are placed in a mold to form the engaging member 92 by injection molding. Thus, the engaging member 92 is integrally formed with the magnetic hub 91 and the shaft 93 as a single monolithic member to prevent disengagement therebetween. However, the engaging member 92 is liable to deform due to overheating during high speed rotation of the rotor 9, resulting in poor rotational balance as well as disengagement between the magnetic hub 91, engaging member 92, and shaft 93. Thus, the overall engaging stability of the rotor 9 is still insufficient. Thus, a need exists for an improved rotor that overcomes the disadvantages encountered during actual use of the conventional rotors 5, 6, 7, 8, and 9.